Inkjet recording methods are such methods that recording is performed by ejecting and depositing droplets of a recording liquid (ink) onto recording media such as paper. According to a method in which an electrothermal converter, as ink-ejecting energy supplying means, is used to provide thermal energy for the ink so as to produce bubbles to eject ink droplets by means of the bubbles, a high-density multi-orifice recording head can be easily realized and high-resolution and high-quality images can be recorded at a high speed (Japanese Patent Publication Nos. S61-59911, S61-59912, S61-59914).
However, inks conventionally used in inkjet recording generally include water as a main component and a solvent with a high boiling point, such as glycol, for the purpose of preventing the inks from drying and clogging. And when recording is performed on plain paper using such inks, inks can sometimes penetrate the inside of recording paper, resulting in insufficient image density or non-uniform image density, which may be attributed to non-uniform distribution of loaded fillers or sizing agents on the surface of the recording medium (recording paper).
Particularly when intending to produce color images, since a plurality of different color inks are overlapped one by one, color inks can sometimes spread or be non-uniformly mixed (hereinafter this phenomenon is referred to as bleeding) at the boundaries between images of different colors, and thus the resultant images are not satisfactory ones.
As means for prevent ink bleeding, disclosed is use of an ink which includes a compound for improving the penetration of the ink, such as a surfactant (Japanese Patent Application Laid-Open No. S55-65269). This method certainly improves the penetration of ink into recording paper and prevents bleeding to some extent, but on the other hand, it allows the colorants in the ink to penetrate deep into the recording paper, which causes such problems as decrease in image density or sharpness or strike-through of images on the back side of the recording medium. Furthermore, since it improves the ink wettability on the surface of the recording paper, ink is more likely to spread, which unfavorably causes decrease in resolution or occurrence of feathering.
There are also disclosed methods in which a liquid that contributes to production of better images is deposited on recording paper prior to ejection of a recording ink. For example, a method is disclosed in which a solution of a polymer such as carboxymethyl cellulose, polyvinyl alcohol or polyvinyl acetate is ejected onto recording paper before printing (Japanese Patent Application Laid-Open No. S56-89595). This method might cause a problem of poor fixing properties of ink because the solution itself is poor in dry-ing properties, though it can prevent bleeding.
To overcome the above described problem, there are disclosed methods: in which recording is performed by applying, on recording paper a liquid containing an organic compound that has 2 or more cationic groups per molecule and then applying an ink containing an anionic dye thereon (Japanese Patent Application Laid-Open No. S63-29971); in which recording is performed by applying an acidic liquid containing, for example, succinic acid on recording paper and then applying an ink thereon (Japanese Patent Application Laid-Open No. S64-9279); and in which a liquid that makes a dye insoluble is applied on recording paper prior to recording (Japanese Patent Application Laid-Open No. S64-63185).
In any one of the above described methods, bleeding can be prevented to some extent. However, it is after a reaction liquid has penetrated into a recording medium that coloring ink is provided onto the recording medium, and therefore, when coloring ink is provided, the reaction liquid is present in the inside of the recording medium, but not on the surface thereof, and almost all the reaction occurs in the inside of the recording medium. This results in problems of insufficient color development and strike-through, which is such a phenomenon that the colorant can be recognized on the back side of the recording medium.
As described above, there is a fear that when ink is reacted with a reaction liquid on the surface of a recording medium, it will not fix on the medium satisfactorily, whereas when ink is reacted with a reaction liquid in the inside of a recording medium, it will not develop color satisfactorily.
There is also a proposal in which reaction of polyvalent metal ions and carboxyl groups is used to prevent bleeding (Japanese Patent Application Laid-Open No. H5-202328). In this case, though bleeding is effectively prevented by the reaction of a polyvalent metal ink and carboxyl groups, there still remains a fear that when coloring ink is highly penetrative to the recording media, problems will occur of decreased color development and strike-through, because the liquid containing polyvalent metal ions are first impregnated into the recording medium and then reacted with coloring ink. Thus, this proposal lacks viewpoint of color development and still has the problem to be solved toward increase in color development, though it is effective in preventing bleeding.